CHARGE TRANSPORT AND LIGHT ABSORPTION IN CONJUGATED SYSTEMS FROM EXTENDED HÜCKEL METHOD AND MARCUS THEORY

Abstract

A simple first principle model was developed based on extended Hückel-type orbital calculation, Marcus electron transport theory and two-dimensional-electron-gas model for the treatment of charge transport in conjugated polymers. Though simple and easy to compute, the effect of the applied electric-field is factored in. Based on this, a complete one-dimensional device model with a single layer of conjugated polymer sandwiched between two electrodes was developed with poly(3-hexylthiophene) (P3HT) as a case study. Simulated J-V curves show that π-π charge transport is much more pronounced than intra-chain transport, hence agree with previous findings. Using the same framework, we also calculated the absorption spectra of P3HT by considering the electronic energy barrier for electronic transitions that would satisfy Franck–Condon principle. Absorption spectra closely harmonize to experimental UV-Vis result. The model also reveals intra-chain electronic transitions to be the dominant absorption mechanism. All parameters of the model are obtained from either ab-initio Density Functional Theory (DFT) or Molecular Dynamics (MD) calculations, so that this model is capable of predicting charge transport and light absorption properties of new conjugated polymers without introducing fit parameters.